A cascade refrigeration cycle apparatus comprises a housing. The housing comprises a high-temperature-side refrigeration circuit communicating with a high-temperature-side compressor, a four-way switching valve, a refrigerant-side flow channel of a water-refrigerant heat exchanger, a high-temperature-side inflation device and a high-temperature refrigerant flow channel of a cascade heat exchanger via a refrigerant pipe, and a low-temperature-side refrigeration circuit communicating with a low-temperature-side compressor, a four-way switching valve, a low-temperature refrigerant flow channel of a cascade heat exchanger, a low-temperature-side inflation device and an air heat exchanger via the refrigerant pipe. A hot-water pipe comprising a pump is connected to a water-side flow channel of the water-refrigerant heat exchanger.
A refrigerant discharged from the low-temperature-side compressor of the low-temperature-side refrigeration circuit is guided to the low-temperature refrigerant flow channel of the cascade heat exchanger, and generates condensation heat. This condensation heat is absorbed in the high-temperature refrigerant flow channel of the cascade heat exchanger in the high-temperature-side refrigeration circuit. Heat is released in the refrigerant-side flow channel of the water-refrigerant heat exchanger. Water or hot water inside the hot-water pipe connected to the water-side flow channel of the water-refrigerant heat exchanger is heated.
Jpn. Pat. Appln. KOKAI Publication No. 2007-198693 describes a cascade refrigeration cycle apparatus.
Recently, in order to more efficiently conduct a warming operation, people attempt to produce a combined cascade refrigeration cycle apparatus in which two cascade refrigeration cycle apparatuses are connected to a hot-water pipe in series or in parallel.
In this combined cascade refrigeration cycle apparatus, an air heat exchanger is used as an evaporator in a low-temperature-side refrigeration circuit. The refrigerant guided to the air heat exchanger evaporates through heat exchange with external air. Therefore, when the temperature of external air becomes extremely low, the fluid contained in external air freezes, turns to frost, and is attached as it is.
Naturally, a defrosting operation is required. As a defrosting system, there is a reverse cycle defrosting system which switches each four-way switching valve of a high-temperature-side refrigeration circuit and a low-temperature-side refrigeration circuit. Apart from this, a hot-gas defrosting system which bypasses the discharged refrigerant of a compressor of a low-temperature-side refrigeration circuit trough a cascade heat exchanger and guides the refrigerant to an evaporator can be considered.
The former system has the advantage of completing a defrosting operation in a short time since hot water of a user side is a heat source. However, there is the problem of decreasing the temperature of hot water outlet to the temperatures lower than the temperature of inlet. This problem is not caused in the latter system. However, since the latter system lacks a heat source required for a defrosting operation, defrosting time increases. As a result, the time in which hot water cannot be warmed up increases.
In these circumstances, there is demand for a combined cascade refrigeration cycle apparatus comprising the following structures: although two cascade refrigeration cycles are provided, the structures of the apparatus are simplified and a defrosting operation can be completed in a short time while decreasing the temperature of water or hot water flowing though a hot-water pipe as little as possible.